1. Field of the Invention
This invention relates to a grain cleaning apparatus and, more particularly, this invention relates to a grain cleaning apparatus having a plurality of discrete cleaning sections with external ducts for bypassing foreign material around the grain flow path in each section.
2. Description of the Prior Art
In grain handling operations, it is frequently necessary to reduce the amount of relatively small foreign material, such as dust, chaff, etc., mixed with grain before storage or shipment thereof. For example, removal of foreign material from grain can increase the efficiency of grain dryers because moisture is typically preferentially absorbed by foreign material. Further, grain cleaning is desirable before storage because small foreign material tends to accumulate in the gaps between particles of stored grain to obstruct air flow through the grain from aeration systems.
Additionally, grain cleaning may be necessary to ensure that the maximum levels of foreign material permitted under the regulations of the Federal Inspection Grain Service Division of the U.S. Department of Agriculture are not exceeded. If the amount of foreign material in grain exceeds those levels, a shipment of grain is "docked" to result in a net loss of income to the shipper.
One form of grain cleaner which has achieved widespread acceptance utilizes gravity flow of grain over a series of screens within an upstanding housing. Grain flows through an inlet at the housing's upper end and is directed outwardly and downwardly over a first layer of screens. Relatively small particles of foreign material fall through the screens into a first foreign material chamber communicating with a foreign material outlet at the housing's lower end.
Grain reaching the outer periphery of the first level of screens reverses its direction of flow and is directed downwardly and inwardly over a second layer of screens overlying a second foreign material receiving chamber, also communicating with the foreign material outlet. Relatively clean grain is received at the bottom of the second level of screens and is directed to a clean grain outlet chute which communicates with a storage facility, vehicle or other grain receiving means.
Such a grain cleaner is typically an integral part of a continuous grain handling system, and may be disposed between a dry elevator leg and a grain storage tank, or between a wet elevator leg and a grain dryer, for example. If relatively clean grain, not requiring cleaning, is to be transferred through a system having a grain cleaner, it may be desirable to bypass the cleaner's screens by means of external lines or integral bypass means.
One form of grain cleaner of the type described above is generally in the shape of two back-to-back pyramids, where each pyramid is defined by four screens in the shape of truncated triangles. Screening occurs on four sides of the cleaner, thus permitting maximum screening to occur through a given vertical distance so as to minimize cleaner height. However, because the screens are in the shape of truncated triangles, corners along the wide side of the screens may be under-utilized.
Two forms of this type of cleaner are described in Hannie et al. U.S. patent application Ser. No. 24,057 filed Mar. 26, 1979, the details of which are hereby incorporated by reference. In the cleaners described in Hannie et al. application Ser. No. 24,057, foreign material is discharged from an upper chamber to a lower chamber through a chute at the bottom of the upper chamber which extends through one of the lower screen layers. In high throughput conditions, however, this chute is a significant obstruction in the second screen layer and thus hinders the flow of grain, thereby reducing capacity.
Other types of grain cleaners have been used in which only one or two sides are used for screening. Such cleaners have limited bushel per hour cleaning capacities since the screening area is relatively small, since screening is limited to, at most, two sides. If the length of the screens along the cleaning sides is increased to increase capacity, the overall height of the unit is correspondingly increased by as much as two feet or more.
Similarly, an increase in screen width to increase capacity results in a corresponding increase in cleaner width. A substantial increase in cleaner height or width is a disadvantage, since the space available in most elevator installations for grain cleaners is limited.